Is Hydro A Renewable Energy?

What is Hydro Power?

Hydro power, also called hydroelectric power, is the process of generating electricity by harnessing the kinetic energy of flowing water. It is considered a renewable energy source because it relies on the water cycle to replenish the water in rivers and reservoirs.¹

Most hydro power plants use dams to store river water in a reservoir. When the water is released from the reservoir, it flows through turbines, causing them to spin. The spinning turbines turn electromagnets that generate electricity. The electricity is then fed into the electrical grid and distributed to homes and businesses.²

So in summary, hydro power utilizes the natural flow of water, often regulated by dams, to generate renewable electricity that is integrated into the electrical grid system. It harnesses the kinetic energy from falling or fast-moving water to spin turbines and generate power.

The Renewability of Hydro

Unlike fossil fuel sources like coal, oil, and natural gas that are finite energy sources, the energy of hydropower is continuously replenished by the water cycle. Rain and snow regenerate the water supply stored behind hydroelectric dams and allow its reuse for power generation over and over again (https://www.energy.gov/eere/water/hydropower-basics). Water is thus a renewable resource, though the systems to capture and harness its energy require infrastructure with environmental impacts. The supply of flowing water can be considered a renewable energy source, but the dams, reservoirs, and other infrastructure required to facilitate hydroelectric generation do have environmental costs and impacts.

In contrast to fossil fuels that take millions of years to form and will eventually be depleted, the water cycle circulates freely in different states between the atmosphere, land, and bodies of water. The Sun’s energy powers evaporation, condensation, and precipitation of water around the globe. This renewable cycle ensures available water resources for hydropower (https://www.usgs.gov/special-topics/water-science-school/science/hydroelectric-power-advantages-production-and-usage). However, hydroelectric facilities and their operation can have significant effects on surrounding ecology and habitats.

Types of Hydroelectric Facilities

There are three primary types of hydroelectric facilities:

• Run-of-river – These facilities channel a portion of a river’s water through a canal or penstock to spin turbines and generate electricity. They do not require dams or water storage reservoirs (Energy.gov, 2022).
• Reservoir/dam – These impoundment facilities use dams to store river water in a reservoir. The water released from the reservoir flows through turbines to generate electricity. They allow control over water flow for power generation (Hydropower.org, 2022).
• Pumped storage – During periods of low electricity demand, excess generation capacity is used to pump water from a lower reservoir to an upper reservoir. During periods of high demand, water is released from the upper to the lower reservoir to generate electricity (Enelgreenpower.com, 2022).

Run-of-river facilities have less environmental impact as they do not require dams or alter the natural flow of the river. Reservoir/dam facilities allow more control over electricity production by storing water.

Global Hydroelectricity Production

China leads the world in hydroelectricity generation, producing over 1,274 billion kilowatt-hours in 2021 according to Statista. Canada comes in second producing 377 billion kWh, followed by Brazil at 363 billion kWh. The United States generates around 260 billion kWh annually.

Overall, hydropower accounts for around 16% of global electricity production. The top countries for hydroelectricity generation tend to have massive rivers and favorable geography like Canada’s Niagara Falls or the Three Gorges Dam in China. Developing countries are rapidly expanding their hydropower capacity to meet rising electricity demand. The International Energy Agency (IEA) forecasts global hydropower generation will grow by 2.4% per year through 2040, led by China, India, Turkey and Ethiopia.

While most major rivers in developed countries like the U.S. and Canada are already dammed, developing nations in Africa, Asia, and Latin America still have significant potential for new projects. For example, the Global Economy reports that the Democratic Republic of the Congo has the potential to produce 100 gigawatts from its rivers but has only developed around 2.5 gigawatts so far.

Pros of Hydro Power

Hydroelectric power is considered a renewable energy source because it uses the earth’s water cycle to generate electricity. As long as there is flowing water, hydroelectric power can be produced without depleting any resource (Benefits of Hydropower – Department of Energy). The fuel for hydroelectric generation is water, which is not consumed in the process.

Hydroelectric power provides reliable electricity generation. The flow of water past the turbines and dams can be controlled and adjusted to meet changing electricity demands. Large reservoirs behind dams also enable hydroelectric plants to store potential energy by pumping water uphill into the reservoir when electricity demand is low. This stored water can then be released through the turbines to produce extra electricity during periods of high demand (All the benefits of hydropower – Enel Green Power).

Dams and reservoirs associated with hydroelectric plants provide opportunities for flood control. Excess water can be held back in the reservoir during heavy rainfall or spring snowmelt, and then released under controlled conditions. This helps prevent downstream flooding. Reservoirs act as a buffer against both floods and droughts (USGS: Hydroelectric Power Advantages).

Cons of Hydro Power

While hydroelectric power has many benefits, it also has some significant drawbacks that should be considered. One major con is that hydroelectric dams disrupt river ecosystems. By stopping the natural flow of a river, dams prevent nutrients from flowing downstream and enable sediment to build up behind the dam. This can destroy spawning grounds for fish like salmon and impact other wildlife that depends on the river.

Another con is that the reservoirs created by hydroelectric dams can emit methane, a potent greenhouse gas. Organic material like vegetation can decay in the oxygen-deficient waters behind a dam, releasing methane into the atmosphere. Some studies have found that certain hydroelectric reservoirs emit more methane per unit of electricity generated than power plants running on fossil fuels. This undermines the perception of hydro as a completely “green” energy source.

Overall, the ecological impacts of disrupting natural waterways and altering sediment patterns are some of the main drawbacks of hydroelectric projects. Mitigation measures like fish ladders can help, but hydropower still fundamentally changes the natural state of rivers. Carefully weighing the trade-offs is important when evaluating dams and reservoirs.

Environmental Impacts

Hydroelectric dams and reservoirs inevitably alter the environment both upstream and downstream. According to the U.S. Geological Survey (USGS), damming rivers causes “large environmental impacts by changing the environment and affecting land use, homes, and natural habitats” (1).

One major environmental impact is habitat destruction from flooding upstream of the dam. As the USGS notes, reservoirs created by hydroelectric dams flood large areas of land that serves as habitat for plants and animals. Flooding forests, wetlands, and other ecosystems can destroy habitats critical for the survival of many species.

Hydroelectric facilities also impact water quality. As the U.S. Energy Information Administration (EIA) states, “Water passing through a dam turbine can cause turbulence and introduce air into the water, lowering its oxygen content” (2). Reduced oxygen harms fish and other aquatic life downstream. Sediment buildup in reservoirs also impacts water quality.

Another key environmental impact is the disruption of fish migration and spawning. As dams block the natural flow of rivers, they present a barrier for migratory fish trying to reach their upstream spawning grounds. Fish ladders and other passage facilities only partially mitigate this effect.

While hydroelectric power has advantages as a renewable energy source, facilities must be carefully designed to minimize their environmental footprint through mitigation strategies.

(1) https://www.usgs.gov/special-topics/water-science-school/science/hydroelectric-power-water-use

(2) https://www.eia.gov/energyexplained/hydropower/hydropower-and-the-environment.php

Mitigating Environmental Harm

While hydroelectric power is a renewable energy source, the dams and reservoirs required for hydroelectric generation can negatively impact the environment in several ways. However, steps can be taken to mitigate some of these harmful effects.

One method is the construction of fish ladders, which allow migratory fish to bypass dams when swimming upstream to spawn. According to the Federal Energy Regulatory Commission, fish ladders have been very successful in reducing the blockage of fish migration routes caused by dams [1].

Another approach is habitat restoration projects around hydroelectric facilities. These can include creating wetlands, restoring forests, and other conservation efforts that benefit local ecosystems. For example, Duke Energy implements several habitat improvement initiatives at its hydropower reservoirs [2].

Lastly, installing more efficient turbines, like Kaplan turbines, can reduce the amount of land that needs to be flooded for a hydroelectric reservoir. Limiting flooded acreage lessens the environmental impact. Modern turbine designs also allow more targeted water flow, further decreasing habitat destruction [3].

The Future of Hydro Power

There is still significant untapped global potential for hydropower, especially from smaller scale and run-of-river projects. According to the International Energy Agency (IEA), global hydropower capacity could increase by 17%, or 230 GW, between 2021-2030 https://www.iea.org/energy-system/renewables/hydroelectricity. Much of this growth is expected to come from new projects in developing countries in Asia, Africa and South America.

Run-of-river hydro projects divert a portion of a river’s water through a channel or pipe to turbines that generate electricity without the need for dams or reservoirs. These projects have a smaller environmental footprint and the flexibility to generate power during high demand periods. According to the Department of Energy (DOE), technologies like adjustable speed turbines and advanced controls are enabling growth in run-of-river hydropower in the U.S. https://www.energy.gov/articles/hydropower-vision-new-report-highlights-future-pathways-us-hydropower.

Conclusions

In reviewing the pros and cons of hydroelectric power, it’s clear that it offers significant advantages as a renewable energy source but also comes with environmental costs. On the pro side, hydro harnesses the renewable power of flowing water to generate large amounts of electricity in a sustainable way. It’s also flexible, reliable, and helps avoid fossil fuel emissions. However, damming rivers can negatively impact local ecosystems and wildlife habitats. There are also concerns around methane emissions from reservoirs and sediment buildup.

Overall, hydro will continue to play a major role in renewable energy futures. It offers baseline power generation and grid stability in ways that intermittent sources like wind and solar cannot. With proper planning and mitigation strategies, the environmental impacts of hydro can be minimized. But ultimately there are ecological tradeoffs. Hydro harnesses incredible power but also fundamentally alters river systems. Renewable energy portfolios will likely require a mix of sources, with hydro as a key component for stability and renewable baseload power.